William, Kate and Harry opened up their initiative to leaders from across UK society, from media and technology firms through to business and the voluntary sector, to become supporters of their project.

Heads Together, spearheaded by the three royals, aims to change the national conversation on mental well-being to a positive one, and is a partnership between eight charities that provide front-line mental health support.

During their last major Heads Together event, the royal trio marked World Mental Health Day last October by making an impassioned plea for society to recognise that psychological problems are suffered by all, and the sooner everyone reaches out to help the better.

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William, Kate and Harry lead the mental health campaign Heads Together

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The Royal trio want to tackle the stigma surrounding mental health

The umbrella organisation is the charity of the year for the 2017 London Marathon, and Heads Together says it wants to use this privileged position to further tackle the stigma surrounding mental health.

During the event in central London, the Cambridges and Harry met guests and gave short speeches setting out their ambitions for Heads Together during the year.

A round-up of the brother-royals, Prince Harry and Prince William.

The royal trio and other speakers previewed some of the themes and initiatives people can expect to see in the months ahead.

The main goal of the campaign – in the run up to the marathon – will be to show people how important it is to start a conversation with a friend, family member, colleague, or a professional when dealing with a mental health challenge.